Résumé : The breakup of 12Be into 6He + 6He and 4He + 8He has been studied using a 378 MeV 12Be beam inelastically excited by 12C and (CH2)n targets. The measurements indicate that breakup occurs from rotational states in the 10 to 25 MeV excitation energy interval, with spins in the range of 4ℏ to 8ℏ. The inferred moment of inertia is consistent with the cluster decay of an exotic molecular structure in 12Be, which may be associated with an α-4n-α cluster configuration.